Day, Night, and Seasons: Why the Sky Changes

Earth spins like a top. The side facing the Sun experiences day, and the side facing away experiences night. Simple enough.

Seasons are the part many beginners get wrong. Summer is not caused by Earth being much closer to the Sun. Instead, Earth’s axis is tilted. When your hemisphere leans toward the Sun, sunlight hits it more directly and days are longer—so it warms up. When it leans away, sunlight is less direct and days are shorter—so it cools down.

This is also why seasons are opposite in the Northern and Southern Hemispheres. While one half of Earth is getting more direct sunlight, the other half is getting less.